An example of a device in which a virtual machine which operates on a physical computer is migrated to another physical computer when an event, such as a failure or a high load, occurs is described in patent document 1 and patent document 2.
In patent document 1, a management server which replaces a virtual server operating on a physical server in which a failure occurs with another virtual server operating on another physical server and makes the virtual server operate on the another physical sever is described. The management server disclosed in patent document 1 selects the virtual server which has the highest priority and whose amount of used resources is equal to or greater than that of the used resources of the virtual server to be moved among the virtual servers with lower priority than the virtual server to be moved. The used resources are performance of a processor and a memory capacity. The management server designates the physical server on which the selected virtual server operates as a movement destination of the virtual server to be moved. The management server designates the selected virtual server as the virtual server to be moved next and repeats the same process. The management server stops the operation of the virtual server which has low priority and for which there is no physical server designated as the relocation destination.
In patent document 2, a management computer which migrates a virtual server to another physical server when a migration trigger for the virtual server is detected is described. For example, the migration trigger for the virtual server is that an index value of a load of the virtual server exceeds a threshold value. The management computer selects a migration destination of the virtual server that is a migration object and a migration path on the basis of a migration path group set in advance, the past and current migration status of each physical server, and the like. The migration path is determined on the basis of a degree of coincidence of system configurations or whether or not the storage devices to be used are identical. The management computer migrates the virtual server that is the migration object on the basis of the migration destination and the migration path that are selected.    [Patent document 1] Japanese Patent Application Laid-Open No. 2009-252204    [Patent document 2] Japanese Patent Application Laid-Open No. 2011-232916